Australia's Science Forum

Decanted Sulphuric acid concentrated, put into a smaller dropper bottle for student use, goes dark colour after some time. Is it still OK to use?
Used for ester preparation.

Thanks
Rosalie (another one)

I have never had mine go a dark colour. Perhaps it is reacting with the dropper? I store mine with just the cap (from serrata I think) and then swap it for a dropper when required. In NSW only teachers are allowed to use the conc acid so for the ester prac the teacher (or sometimes me) adds the drops but the kids do the rest.

The acid is still fine. The colour of conc Sulphuric ranges from colorless to dark brown depending on the level of contaminants, but will still work ok for ester production and most school purposes.

Concentrated sulfuric acid should not decompose over time, unless it has been contaminated. Going brown is a likely sign that it is oxidizing something; check the glass or stopper.

It is still OK to use. Mine went off white (brandy) colour and worked fine.
Lada

I used to analyze concentrated sulfuric acid straight from the acid plant in an industry I worked in - it was a thick dark treacle colour - and boy did it burn!! the clear liquid stuff is innocuous in comparison!

Last week I was getting something out of the corrosives cupboard and noticed the white powder is back coating the bottom of the cupboard. I picked up one of the smaller botttles of conc. sulfuric. As i was squating and my knees hurt I didn't initially think much of the pin prick sensation on my leg. Then I looked down and my stockings were melting off my legs. Had to whip them off and go bare legged for the rest of day. Not a good look but I was glad that the stockings were the only casuality. Still not real sure where the drips were coming from but suffice to say that bottle is gone.

Thanks for the replies.
So is OK to use and I don't have to worry about disposal. Can use it to make a carbon pillar with sugar!

Rosalie (another one)

I can't see why not! Give it a go At least it is in a fume cupboard (make sure the sides are down!) so you're safe if it doesn't work!

Hi All,

Mostly darkens due to Pb in glass...

Lead in levels where is it neglegible, but over time causes the acid to darken..

If you look carefully the hint of dull grey will be apparent.

Cheers,

Robb.....

I have some rather old bottles of conc Sulphuric acid that the labels have discoloured and they seem to be "sweating", even though some have not been opened and still have tape around the top. Is it OK under the rules to take these labels off and put new GHS labels on them?

My worry is that they will sweat and just ruin the new labels. They are currently in 500mL bottles and on the shorter top shelf - I could decant it into a winchester - but in my current corrosive cupboard I don't have a lot of space on the smaller bottom shelf - and it's barely high enough to fit winchesters anyway.

Thanks

Do not transfer the small bottles into a large one. Much harder to handle. If they are passed resurrection, either neutralize the bottle and dispose or keep for collection later. Acid is still good to use for junior experiments and reflux for seniors.
Lada

I've found some dark brown Conc sulphuric acid here. It didn't react with sugar for the carbon snake demo (which is what I got it out for). Is it likely to be good for anything? There is probably about 1L of it.

Follow up on my previous post - I was looking up how to dispose of it when I found the amounts for use to make the carbon snake. (As far as I know, most teachers just do "about this much sugar" and add "about that much acid" and off it goes!). I thought I should try it in case our quantities were just way out. It worked - but VERY SLOWLY! It took about 10 mins before it started growing and it wasn't nearly as spectacular as I remember it to be... so, is it worth keeping this acid or do you think I should just dispose of it? The only thing I can think of to do with it is to keep it for a comparison of concentration and reaction times.

neutralize it with Sodium Carbonate, until it stop's Fizzing up, if you know want I mean. Do this in a fume cupboard.